Chapter 7
Designing Mechanical
Systems
Six Simple Machines
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Pulley
Wheel and Axle
Inclined Plane
Wedge
Screw
Lever
Machines and Tools
• Machines and tools are mechanical devices
that work by transmitting or converting
energy.
• Machines are made up of a variety of
mechanisms.
• What are some examples of machines.
Mechanisms
• Help extend human capability by creating
some desired output or motion.
• Takes an input motion or force and creates a
desired output or force.
•Lever
•Gear
•Crank
•Cam
•Wheel
•Screw
Kinematics
• The study of motion without regard to the
forces or mass of the things moving.
• Kinematic diagrams are scaled drawings
symbolizing how mechanisms work.
• Page 143 (fig. 7-7)
Motion
• Common types of motion:
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Linear
Reciprocal
Rotary
Oscillating
Levers and Linkages
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Fulcrum
Load
Effort
Classes (p. 146)
– First
– Second
– Third
Mechanical Advantage
• The ratio between the load and effort.
• Deals only with forces.
• Mechanical Advantage > 1 means that the
output force will be greater than the input
force. (But the input distance will need to be
greater than the output distance.)
Velocity Ratio
• Deals with the distance gained or lost due to
a mechanical advantage.
• Velocity Ration >1 means that the input
distance (or effort) to move a load will be
greater than the output distance of the load.
Linkages
• Linkages transmit the motion or force to the
desired output location.
• Linkages:
– change the direction of the force
– Change the length of motion of the force
– Split the motion and force over multiple paths
Linkages (cont.)
• Parallel Linkages
• Treadle Linkages
• Toggle Linkages
Rotary Mechanisms
• Gears, Pulleys, Cams, Ratchets, Wheels,
etc.
• These transfer of change input rotational
motion and force to output motion and
force.
• Output force can be either rotational or
reciprocating.
Gears
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Toothed wheels fixed to an axle.
Drive gear – connected to the input axle.
Driven gear – connected to the output axle.
Gear train – when an number of gears are
connected together.
Gear Ratio =
Number of driven teeth (output)
Number of driver teeth (input)
Gear Types
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Spur
Helical
Worm
Bevel
Rack and Pinion
Belts/Pulleys & Chains/Sprockets
• Use belts and chains to convert motion and
force.
• Uses same measures of Mechanical
advantage and Velocity Ratio as gears.
Cams
• Eccentric cams – circular disk with the axle
placed off center.
• Pear shaped devices that convert rotary
motion into reciprocating motion.
• Cams use followers to conform to their
shape and cause motion.
Others
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Cranks and sliders
Ratcheting mechanisms
Clutches
Brakes